Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.

Hydrogel nanotubes with ice helices entrapped within their internal conduits are a promising material for diabetic wound healing.

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Graphene quantum dots (GQDs) are the harbingers of a paradigm shift that revitalize self-assembly of the colloidal puzzle by adding shape and size to the material-design palette. Although self-assembly is ubiquitous in nature, the extent to which these molecular legos can be engineered reminds us that we are still apprenticing polymer carpenters. In this quest to unlock exotic nanostructures ascending from eventual anisotropy, we have utilized different concentrations of GQDs as a filler in free-radical-mediated aqueous copolymerization. Extensive polymer grafting over the geometrically confined landscape of GQDs (0.05%) bolsters crystallization instilling a loom which steers interaction of polymeric cilia into interlaced equilateral triangles with high sophistication. Such two-dimensional (2D) assemblies epitomizing the planar tiling of “Star of David” forming a molecular kagome lattice (KL) without metal templation evoke petrichor. Interestingly, a higher percentage (0.3%) of GQDs allow selective tuning of the interfacial property of copolymers breaking symmetry due to surface energy incongruity, producing exotic Janus nanomicelles (JNMs). Herein, with the help of a suite of characterizations, we delineate the mechanism behind the formation of the KL and JNMs which forms a depot of heightened drug accretion with targeted delivery of 5-fluorouracil in the colon as validated by gamma scintigraphy studies.

Graphitic carbon nitride (gCN) has only recently experienced a renaissance in a myriad of domains despite existing as a long-established material described in the chemical literature. Notwithstanding the upturn, their conventional synthesis at extremely high temperatures yielding limiting compositions stands in the way of achieving a paradigm shift in gCN fabrication. With the ultimate goal of surpassing these hurdles, we utilize Ndoped carbon nanosheets (N-CNS) as a filler in free-radical-mediated aqueous copolymerization. By dispersing N-CNS in a polymer matrix, high-performance mechanically robust composites could be developed and tailored to individual applications. As-synthesized hydrogel nanocomposite systems are used to decode the balance for emulating evolutionary accomplishments of nature's nanocomposites like the "abalone's nacre". At a lower concentration (0.05%), N-CNS disperse homogeneously and interact intimately with the polymer matrix forming an "interphase" zone around individual nanofillers dramatically affecting the mobility of polymer chains to yield sheet architectures. On increasing the filler concentration (0.3%), the intercalation phenomenon gets perturbed due to an intrinsically oriented aggregation of nanofiller giving rise to a surge in entropy that leads to conspicuous buckling and tubular aggregates. At the interfacial regime, the poly(acrylic acid) domains come in closer proximity to the hydrophobic cages of N-CNS, and a nanoconfinement effect exerts high pressure manifesting acid-catalyzed condensation of melamine units to form, for the first time, quasi-two-dimensional heptazine-gCN (h-gCN) within hydrogel nanocomposites. Polymer properties are enhanced by the addition of N-CNS through complex interfacial interactions and the unique distributions of internanofiller distances. Endowed with mechanical properties that closely mimic natural skin and combined with the repurposed drug "losartan", these hydrogel nanocomposites offer scarless healing of second-degree burns.